The present invention relates to the Chemical branch, and in particular with a new process for obtaining 2-bromo-5-(2-bromo-2-nitrovinyl)-furan, a product of interest for human- and animal health due to its broad activity as microbicide.
2-bromo-5-(2-bromo-2-nitrovinyl)-furan was described for the first time in the international literature by authoress Z. N. Nazarova in 1972 (Z. N. Nazarova, 1972. xe2x80x9cSynthesis of some furylnitroolefins with potential biological activity; Khim. Farm. Zh. 6(10,) pp. 5-8 and Z. N. Nazarova et al, 1972. xe2x80x9cPhysicochemical properties and reactivity of furylnitroolefins, Zh. Org. Khim. 8 (2), pp. 404-11).
Studies regarding the procedure for obtaining this product in a very pure form and with good yields, including its in vitro and in vivo actions, as well as pharmaceutical compositions containing said product, have been previously described (Canadian Patent No. 2,147,594).
The present invention is related to a novel procedure for obtaining 2-bromo-5-(2-bromo-2-nitrovinyl)-furan wherein the reaction is maintained by direct action of bromine to 2-nitrovinylfuran suspended in carbon disulfide. The novelty in this step is based on the addition of charcoal during the synthesis and the decreased quantity of solvent required. Normally, charcoal is used as a purifier due to its adsorptive properties. However, in the present invention charcoal acts as a catalyzer of the reaction. This is a new discovery. It is inventive and not obvious.
In a preferred embodiment of the process of this invention direct bromination of 2-nitrovinylfuran in a molar relation 1:2to 1:2.6 in carbon disulfide is carried out during periods of 1 to 3 hours, with temperature regulated in a range from 20 to 60xc2x0 C., adding, from the beginning of the reaction, between 40 to 80% of charcoal in relation to the 2-nitrovinylfuran mass, followed of neutralization and dehydrobromination with pyridine at temperatures between 40 and 60xc2x0 C., with subsequent purification of the product with ethanol and charcoal.
The addition of charcoal is advantageous because the reaction is no longer exothermic, which is evidenced in the constant temperature of the reactor and there is no emission of bromine through the condenser and the flask traps.
Neutralization and dehydrobromination of 2-bromo-5-(2-bromo-2-nitrovinyl)-furan contained in the reaction mixture is carried out with pyridine dissolved in carbon disulfide in very short time and without risks as the temperature is not increased to any great extend.
At the completion of this step, the product is filtered under heating and the solution is allowed to crystallize between xe2x88x9210 and xe2x88x9225xc2x0 C. during 10-15 hours. This crude product has a higher purity (95%) than the obtained from the former technique (80%).
The crystals of crude product are purified by hot dissolution with ethanol and the addition of charcoal, finally the crystals obtained are recrystallized with ethanol.
In the reaction step gas absorption traps are connected to the reactor in order to absorb the hydrogen bromine that is liberated with the purpose of forming bromhydric acid. In this way, it does not escape to the environment and therefore it can be captured and marketed. Consequently, using the process of the present invention the volume of residuals is considerably reduced (by half) in comparison with known techniques. Furthermore, such residuals can be recovered with water traps and can be re-used due to their low level of contamination with bromide.
With this new process, the distillation step of the carbon disulfide excess, that always contained bromine, is eliminated. This decreases the process in general and the treatment of this aggressive residual is unnecessary.
After the purification process the product is the same as that obtained with the preceding technique, (Z)-2-bromo-5-(2-bromo-2-nitrovinyl)-furan; however the purity is grater than 99%.